EP0132863A1 - Circuit de protection - Google Patents

Circuit de protection Download PDF

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Publication number
EP0132863A1
EP0132863A1 EP84200884A EP84200884A EP0132863A1 EP 0132863 A1 EP0132863 A1 EP 0132863A1 EP 84200884 A EP84200884 A EP 84200884A EP 84200884 A EP84200884 A EP 84200884A EP 0132863 A1 EP0132863 A1 EP 0132863A1
Authority
EP
European Patent Office
Prior art keywords
current
voltage
transistor
collector
emitter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP84200884A
Other languages
German (de)
English (en)
Other versions
EP0132863B1 (fr
Inventor
Evert Seevinck
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Philips Gloeilampenfabrieken NV, Koninklijke Philips Electronics NV filed Critical Philips Gloeilampenfabrieken NV
Publication of EP0132863A1 publication Critical patent/EP0132863A1/fr
Application granted granted Critical
Publication of EP0132863B1 publication Critical patent/EP0132863B1/fr
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/52—Circuit arrangements for protecting such amplifiers

Definitions

  • the invention relates to a protection circuit for protecting a transistor from overloading, comprising
  • Such a protection circuit can, for example, be used in integrated power amplifiers for audio equipment.
  • the output transistors of such power amplifiers must be operated within the Safe Operating Area Rating (SOAR) to prevent the transistors from being damaged by overloading.
  • SOAR Safe Operating Area Rating
  • the first means comprises a first resistor included in the collector or the emitter lead of the transistor.
  • a first signal is derived from the voltage across this resistor, which signal consequently is proportional to the current through the transistor.
  • the second means comprise a voltage divider formed by second and third resistors and arranged between the collector and the emitter of the transistor.
  • a second signal is derived from the voltage across the second resistor, which second signal is consequently proportional to the collector-emitter voltage of the transistor.
  • knee voltage the voltage across the second resistor is limited by a Zener diode arranged in parallel therewith, so that the second signal has a constant value above the knee voltage.
  • the first and second signals are added together whereafter this sum signal is compared with a threshold value. If the sum signal becomes greater than the threshold value, then a transistor is rendered conductive which diverts base current from the output transistor and consequently limits the current through the output transistor.
  • the limited value of the current through the output transistor is equal to the difference between a fixed current which is proportional to the threshold value and a variable current which is proportional to the collector-emitter voltage of the transistor.
  • the second signal With very small collector-emitter voltages the second signal is so small as to be disregarded. In that case the protection becomes operative if the first signal, which is proportional to the collector current, becomes greater than the threshold value. The implication is that the maximum current through the output transistor is proportional to the threshold value.
  • a small residual current may continue to flow through the output transistor in the event of collector-emitter voltages above the knee voltage.
  • This residual current is necessary to ensure that the circuit can operate correctly upon application of the supply voltage, as the load, for example a loudspeaker, is coupled to the output of the output transistor via a capacitor. Upon switch-on a certain current is required to charge this capacitor.
  • the residual current is also required to prevent distortion of the output signal in the event of a large voltage swing. This residual current is equal to the difference between the maximum current through the transistor, which is proportional to the threshold value, and a fixed current which is proportional to the knee voltage.
  • the residual current is much smaller, for example by a factor of 20, than the maximum current through the output transistor. Consequently, the residual current is formed by the difference between two currents which are each much larger than the residual current itself, in the present example 20 and 19 times larger, respectively. As a result thereof, the residual current is highly dependent on variations in these currents. A variation of, for example, 5% in one of the currents causes a variation of 100% in the residual current. Precisely in the area above the knee voltage with high collector-emitter voltages an excessive residual current may easily result in the output transistor being damaged. Too small a residual current has for its result that the output signal is distorted in the event of a large voltage swing or that the circuit cannot build-up to proper operation upon application of the supply voltage.
  • the residual current through the output transistor is equal to a fixed current, which is variation-dependent to a much lasser extent.
  • the second signal is equal to zero above the knee voltage.
  • Such a protection circuit may be further characterized in that the first means comprise a first resistor included in the collector or the emitter lead of the transistor and a first voltage-current converter converting the voltage across the first resistor into a current proportional thereto, that the second means comprise a second voltage-current converter converting the difference between the collector-emitter voltage and the knee voltage into a current proportional thereto and that the third means comprise a control amplifier which so limits the current through the transistor that the difference between the output currents of the first and second Voltage-current converters is equal to a threshold current carried by a current source.
  • Fig. 1 shows the basic circuit diagram of an example of a protection circuit according to the invention.
  • the output transistor T 1 to be protected is connected by means of its collector to the output 2 of the circuit to which a load impedance 4 is coupled via a capacitor 3.
  • the emitter of transistor T 1 is connected to the negative supply terminal 5, in this case ground, via a resistor R 1 .
  • the resistor R 1 has a very small resistance value of, for example, 0.03 Ohm, which can be constituted by the wire connection between the emitter of transistor T 1 and the supply terminal 5.
  • the transistor T 1 must be operated within the so-called SOAR to prevent the transistor T 1 from being damaged by overloading due to an excessively high current, either in combination or not in combination with an excessively high voltage.
  • the circuit In order to ensure operation within the SOAR-range the circuit must be protected. To that end the emitter current I E of transistor T 1 is converted by resistor R 1 into a voltage which is applied to the non-inverting input 7 of a voltage-current converter 6, whose inverting input 8 is connected to ground.
  • the collector-emitter voltage V CE of transistor T 1 is applied to the inverting input 10 of a voltage-current converter 9.
  • the non-inverting input 11 of this V/I-converter 9 carries a constant voltage V KN , the so-called knee voltage.
  • a diode 12 which is cut-off at the instant at which the output current reverses, that is to say at the instant at which the collector-emitter voltage V CE becomes larger than the knee voltage V KN , is included in the output lead of the V/I-converter 9. Consequently, the V/I-converter 9 does not produce an output current for collector-emitter voltages V CE larger than the knee voltage V KN .
  • the output leads of the V/I-converters 6 and 9 are connected to a common point 13, which is coupled to a current source 14 carrying a current I D and are further connected via a diode 15 to the inverting input 17 of a control amplifier 16, whose non-inverting input 18 carries a drive signal for the output transistor T 1 .
  • the output of the amplifier 16 is coupled to the base of the output transistor T 1 .
  • This current I m is now compared with the current I D carried by the current source 14.
  • Fig. 2 shows the I C /V CE characteristic determined by formulae 2a and 2b. For a very small V CE the current is limited to the maximum current
  • the limit value of the current I E decreases linearly versus increasing VCE .
  • a small residual current which is defined by formula 2b continues to flow through transistor T 1 .
  • This residual current ensures that the circuit is capable of supplying the current required for the quiescent setting when the supply is switched on. For that purpose it is inter alia necessary that upon switch on of the supply voltage a small current flows to charge the capacitor 3 (see Fig. 1).
  • a small residual current must also flow to prevent, in the event of a large voltage swing, distortion which would otherwise occur because of the fact that the transistor T 1 becomes currentless.
  • the residual current is no longer formed, as in the prior art protection circuit, by the difference between two comparatively large currents but is directly determined by the threshold current I D .
  • the magnitude of the residual current depends therefore to a much lesser extent on variations, so that the probability that the output transistor T 1 is damaged by overloading at high collector-emitter voltages is significantly reduced.
  • T 1 is again the transistor to be protected, whose collector is connected to the output 2 and whose emitter is connected to ground via a resistor R i .
  • the resistor R forms part of a current mirror circuit forming the first voltage-current converter.
  • the current mirror circuit comprises a first path, incorporating a current source 20, a diode-connected transistor T 2 , a transistor T 3 and the resistor R, and a second path incorporating transistors T 4 and T 5 and resistor R 2 .
  • the transistors T 2 and T 4 have commonned bases, whilst the base of transistor T 3 is connected to the collector of transistor T 5 and the base of transistor T 5 is connected to the collector of transistor T 3 .
  • the collector current of transistor T 4 is substantially equal to that of transistor T 5
  • the collector current of transistor T 2 is substantially equal to that of transistor T 3
  • the sum of the base-emitter voltages of transistors T 3 and T 4 is qual to the sum of those of transistors T 2 and T 5 .
  • the collector current of transistor T 4 is therefore such that the voltages across the resistors R 1 and R 2 are substantially equal.
  • the emitter current I E of transistor T 1 there will therefore flow in the collector circuit of transistor T 4 , disregarding a setting direct current term due to current source 20, and disregarding the collector current of transistor T 9 , a current which is equal to
  • the direct current term is compensated for by an equally large term in the current carried by current source 25, which however plays no part in the operation of the protection and is consequently omitted from the further calculations.
  • the collector of transistor T 1 is coupled via a resistor R 3 and a diode 21 to the input of a current mirror formed by the transistors T 79 T 8 and T 9 .
  • a current source 22 carrying a current kI D is coupled to the input of the current mirror.
  • the commonned emitters of the transistors T 79 T 8 are connected to the emitter of a transistor T 10 , the base of which carries a reference voltage Y Z .
  • the output current of the current mirror T 79 T 8 , T 9 is applied to the resistor R 2 .
  • the voltage at the cathode of diode 21 is substantially V z - 3V BE , wherein the V BE s are the base-emitter voltages of transistors T 8 , T 9 and T 10 .
  • the diode 21 is therefore non-conductive forvoltages at the output 2 less than V Z - 2V BE .
  • the current applied to resistor R 2 from mirror T 7 , T 8 , T is exactly equal to the current kI D carried by current source 22.
  • the total collector current I M , of transistor T 4 is then equal to
  • This current is now first reproduced with the aid of a current mirror comprising transistors T 11 and T 12 and thereafter compared with the current I D carried by a current source 25, which in this example is further coupled schematically for the sake of simplicity to a control amplifier 27 via a diode 26. If now the current I M becomes greater than the current I D then the protection circuit becomes operative and the control amplifier so controls the current I E through the output transistor T 1 that the current I M becomes equal to the current I D . The current I E is thereby limited to the maximum value
  • FIG. 4 illustrates the associated I E - V CE characteristic together with the characteristic values.
  • Fig. 5 shows an amplifier circuit provided with protection circuits according to the invention.
  • the amplifier comprises a first stage 30 which evidences the character of a voltage-current converter and comprises a pair of transistors T 15 and T 16 which are connected as a differential amplifier and whose base electrodes constitute theinverting and the non-inverting inputs.
  • the emitters of the transistors T 15 and T 16 are connected to the positive supply terminal 32 via a current source 31.
  • the collectors of the transistors T 151 T 16 are connected to the output 36 of this stage 3 0 via a current mirror comprising T 179 T 18 , T 190 resistors 33 and 34 and current source 35.
  • the output 36 forms at the same time the input 36 of a Miller stage 40, which has the character of a current-voltage converter.
  • the input 36 is further connected to output 2 via a compensation-capacitance 46.
  • This stage 40 comprises a control transistor T 20 with emitter resistor 42, which is driven by means of the emitter follower configuration formed by transistor T21 and current source 41 and whose collector is connected to the positive supply terminal 32 via the diodes 42, 43 and 44 and a current source 45.
  • the output stage is constructed as a quasi-complementary output stage with NPN output transistors T 1 and T 25 , which form Darlington transistors with NPN transistors T 26 and T 27 respectively. The quasi-complementary behaviour is obtained by adding the PNP transistors T 28 and T 29 as shown in the Figure.
  • Output transistor T 1 is protected by a circuit 50 which is almost wholly identical to the protection circuit of Fig. 3 and in which corresponding components are given the same reference numerals.
  • the current I M is reproduced with the aid of a current mirror comprising transistors T 30 , T 31 and resistors 51 and 52.
  • the difference between the currents I M and I D is applied to the series arrangement of a resistor 53 and capacitor 54.
  • the voltage across this series arrangement is applied to resistor 55 via the amplifier T 32 which is connected as an emitter follower.
  • the emitter current of transistor T 32 must still be inverted before presentation to the input 36 of the control stage. This is accomplished by connecting the resistor 55 to the input of the current mirror T 17 , T 18 , T 19 , which causes that current mirror to invert the emitter current of transistor T 32 before presenting it to input 36.
  • the base of transistor T 32 is clamped with the aid of a transistor T 33 relative to a point which carries reference voltage V R .
  • This measure has for its object to prevent the protection circuit 50 from becomingactive when there is no need for the protection to operate.
  • the current I m is then smaller than the current I D carried by current source 25.
  • the transistor T is then kept in the conducting stage by the superfluous current from current source 25.
  • the voltage V R is therefore such that transistor T 32 does not conduct when the protection is not active.
  • Transistor T 33 is rendered non-conductive at the instant at which the protection becomes operative and transistor T 32 starts to conduct.
  • Output transistor T 25 is protected in a similar way by means of a circuit 50A, which corresponds to a large extent to circuit 50 and in which corresponding components are given the same reference numerals with the addition of the index A.
  • Themode of operation of circuit 50A is the same as that of circuit 50, with the exception that the transistors of the current mirrors T 2A to T 5A and T 7A to T 10A are of the opposite conductivity types. As a result thereof the current I m must not first be inverted by a current mirror before it is applied to the base of transistor T 32A .
  • the resistor 55A is directly connected to the input 36 of the control amplifier T 20 , T 21Z .

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
EP84200884A 1983-06-21 1984-06-19 Circuit de protection Expired EP0132863B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL8302197A NL8302197A (nl) 1983-06-21 1983-06-21 Beveiligingsschakeling.
NL8302197 1983-06-21

Publications (2)

Publication Number Publication Date
EP0132863A1 true EP0132863A1 (fr) 1985-02-13
EP0132863B1 EP0132863B1 (fr) 1988-03-30

Family

ID=19842040

Family Applications (1)

Application Number Title Priority Date Filing Date
EP84200884A Expired EP0132863B1 (fr) 1983-06-21 1984-06-19 Circuit de protection

Country Status (8)

Country Link
US (1) US4599578A (fr)
EP (1) EP0132863B1 (fr)
JP (1) JPS6014510A (fr)
CA (1) CA1214524A (fr)
DE (1) DE3470262D1 (fr)
HK (1) HK82391A (fr)
NL (1) NL8302197A (fr)
SG (1) SG50490G (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3619230A1 (de) * 1985-06-12 1986-12-18 Sgs Microelettronica S.P.A., Catania Vorrichtung zum schutz der endstufe eines verstaerkers vor kurzschluessen
US5097225A (en) * 1989-07-06 1992-03-17 U. S. Philips Corporation Amplifier with short-circuit protection
EP0709956A1 (fr) * 1994-10-27 1996-05-01 Co.Ri.M.Me. Consorzio Per La Ricerca Sulla Microelettronica Nel Mezzogiorno Méthode et circuit pour protéger un transistor contre la déconnection et régulateur de tension utilisant la méthode

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT1244209B (it) * 1990-12-20 1994-07-08 Sgs Thomson Microelectronics Circuito di controllo di caratteristiche tensione/corrente particolarmente per la protezione di transistori di potenza
JPH07113130A (ja) * 1993-10-18 1995-05-02 Mitsubishi Heavy Ind Ltd 金属Ｎａ封入中空体の処理方法及び装置
DE69902889D1 (de) 1999-06-15 2002-10-17 St Microelectronics Srl Spannungsgesteuerte Treiberstufe mit geregeltem Strom
FR2815196B1 (fr) * 2000-10-06 2003-03-21 St Microelectronics Sa Amplificateur d'erreur integre
SE532467C2 (sv) * 2007-12-27 2010-01-26 Numat As Implantatrengöringsverktyg för rengöring av ett metalliskt implantat
US8841888B2 (en) * 2011-06-16 2014-09-23 02Micro, Inc. Individual cell voltage detection circuit for charge and discharge control in a battery pack

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1222118B (de) * 1965-02-20 1966-08-04 Licentia Gmbh Begrenzungsregelung der Ausgangsleistung von Leistungstransistoren
DE2637270B1 (de) * 1976-08-19 1977-09-29 Standard Elek K Lorenz Ag UEberlastungsschutzeinrichtung
FR2476936A1 (fr) * 1980-02-25 1981-08-28 Philips Nv Circuit d'amplification
US4355341A (en) * 1980-06-30 1982-10-19 Rca Corporation Power protection circuit for transistors

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6223131Y2 (fr) * 1981-05-29 1987-06-12

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1222118B (de) * 1965-02-20 1966-08-04 Licentia Gmbh Begrenzungsregelung der Ausgangsleistung von Leistungstransistoren
DE2637270B1 (de) * 1976-08-19 1977-09-29 Standard Elek K Lorenz Ag UEberlastungsschutzeinrichtung
FR2476936A1 (fr) * 1980-02-25 1981-08-28 Philips Nv Circuit d'amplification
US4355341A (en) * 1980-06-30 1982-10-19 Rca Corporation Power protection circuit for transistors

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3619230A1 (de) * 1985-06-12 1986-12-18 Sgs Microelettronica S.P.A., Catania Vorrichtung zum schutz der endstufe eines verstaerkers vor kurzschluessen
US5097225A (en) * 1989-07-06 1992-03-17 U. S. Philips Corporation Amplifier with short-circuit protection
EP0709956A1 (fr) * 1994-10-27 1996-05-01 Co.Ri.M.Me. Consorzio Per La Ricerca Sulla Microelettronica Nel Mezzogiorno Méthode et circuit pour protéger un transistor contre la déconnection et régulateur de tension utilisant la méthode
US5714905A (en) * 1994-10-27 1998-02-03 Consorzio Per La Ricerca Sulla Microelettronica Nel Mezzogiorno Latch-down-resistant protection circuits and voltage regulator

Also Published As

Publication number Publication date
US4599578A (en) 1986-07-08
SG50490G (en) 1990-08-31
HK82391A (en) 1991-11-01
JPH0525201B2 (fr) 1993-04-12
DE3470262D1 (en) 1988-05-05
NL8302197A (nl) 1985-01-16
JPS6014510A (ja) 1985-01-25
CA1214524A (fr) 1986-11-25
EP0132863B1 (fr) 1988-03-30

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